Monorepo: consolidate 7 repos into one

Combines shared, blog, market, cart, events, federation, and account
into a single repository. Eliminates submodule sync, sibling model
copying at build time, and per-app CI orchestration.

Changes:
- Remove per-app .git, .gitmodules, .gitea, submodule shared/ dirs
- Remove stale sibling model copies from each app
- Update all 6 Dockerfiles for monorepo build context (root = .)
- Add build directives to docker-compose.yml
- Add single .gitea/workflows/ci.yml with change detection
- Add .dockerignore for monorepo build context
- Create __init__.py for federation and account (cross-app imports)

cart/bp/cart/services/get_cart.py

@@ -0,0 +1,25 @@
+from sqlalchemy import select
+from sqlalchemy.orm import selectinload
+
+from shared.models.market import CartItem
+from .identity import current_cart_identity
+
+async def get_cart(session):
+  ident = current_cart_identity()
+  
+  filters = [CartItem.deleted_at.is_(None)]
+  if ident["user_id"] is not None:
+      filters.append(CartItem.user_id == ident["user_id"])
+  else:
+      filters.append(CartItem.session_id == ident["session_id"])
+
+  result = await session.execute(
+      select(CartItem)
+      .where(*filters)
+      .order_by(CartItem.created_at.desc())
+      .options(
+          selectinload(CartItem.product),
+          selectinload(CartItem.market_place),
+      )
+  )
+  return result.scalars().all()